DECsystem-1090 (KL10) power requirements

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Sep 29 03:25:42 1998

Questions came up last week about how much power a DECsystem-1090 CPU (KL10)
consumes, and how the power supply works. Tony Duell suggested that the KL10
might not consume any more power than a big PDP-11/45 system; I disagreed.

My previous description of the power system was not entirely accurate, so I've
dug out some technical documentation, including the manual "Power System
(1080/1090) Interface Description", part number EK-PWR1-ID-002, dated March
1977.

The KL10 CPU cabinet consists of three bays. In a 1080 or 1090, the middle
bay contains the main CPU card cage, which has 47 extended hex modules full
of ECL logic.

The left bay (as viewed from the front) contains an I/O card cage containing
up to 50 extended hex modules full of TTL for the RH20 Massbus channels, DTE20
front-end interfaces, DMA20 memory bus interface, and DIA20 I/O bus interface.

The right bay contains a PDP-11/40 front end processor, a TU56 dual DECtape
transport, and a TC11 DECtape control.

Note that this does not include any memory or peripherals necessary to
make a complete system. I am going to describe only the power requirements
of the CPU cabinet.

All KL10 models require three-phase power. The KL10-AA and KL10-BA models
operate on three phases of 90-132 VAC 60 Hz (208 VAC nominal phase-to-phase)
The KL10-AB and KL10-BB operate on three phases of 180-264 VAC 50 Hz (416V
nominal phase-to-phase). Total input power is specified as 12.6 kW typical
for a basic system; a real-world configuration would have more DTE20 and
RH20 units, so it would consume more power.

Needless to say, the power supplies in the KL10 are not power factor
corrected. The 863 three-phase power control has a 75A main circuit breaker.
Unfortunately I do not have a copy of the DECsystem-10 Site Preparation Guide,
so I don't know what the actual specifications for peak current per phase
are.

With the exception of the power supply for the main CPU cage and the cooling
fans for that bay, most of the machine actually operates on single phase
power. The various fans and power supplies are distributed between the
phases to balance the load.

The CPU cage fans operate between two phases (208V) in the -AA and -BA models,
and between one phase and neutral (240V) in the -AB and -BB models.

The power supply for the ECL consists of an H760A or H760B raw power supply
(depending on the line voltage), a 70-09475 capacitor assembly, and an H761
regulated series pass assembly.

The H760A/B contains three ferroresonant transformers with primaries wired in
a three-phase delta. The secondaries are center-tapped and wired with
half-wave bridge rectifiers. The output is -12V at 490A. The diodes are
mounted to a massive heat sink with its own fans.

The capacitor assembly consists of thirteen 0.3F capacitors in parallel for
a total capacitance of 3.9F. The output under full load is -11V+-10%.
In the event of a power failure, this is sufficient to allow a hold time
of 20 ms before the voltage drops below -7.5V.

The H761 regulated series pass assembly consists of 13 linear regulators.
Nine have -5.2V 35A outputs for the ECL main power, and four have -2V 35A
outputs for ECL termination. There is room for a 14th linear regulator
which is normally not installed.

The maximum load for the CPU card cage is thus (9*5.2V*35A)+(4*2.0V*35A), or
1918W. At that load, the input power required by the power supply is
over 5460W. This is less than 35% efficiency.

Of course, the ECL power supply is nowhere near the whole story.

The following additional power supplies are in the system:

quant model output use
----- ----- ------ --------------
1 H720 +5, -15 DECtape system
1 H725
        
1 H7420 AC power supply PDP-11/40
3 H744 +5
1 H745 -15
1 H754 +20, -5

1 H732 0-20VDC margin check
1 783-C +10, -15

1 H7420 AC power supply
1 H744 +5V CPU cage TTL supply
2 H744 +5V I/O cage DTE20 TTL supply
1 H744 +5V I/O cage RH20 TTL supply

1 H7420 AC power supply
4 H744 +5V I/O cage RH20 TTL supply

1 H7420 AC power supply
1 H770 +15V air flow sensors
1 H745 -15V I/O cage DIA20/DMA20
3 H744 +5 I/O cage DIA20/DMA20 TTL supply

I have not found any figures for typical current used by the various
subsystems. However, the ratings of the regulators are:

H720 5V 22A, -15V 10A, unregulated -22V 1A, unregulated +8V 1.5A
                          (unregulated outputs not used in KL10)
H732 0-20V 5A
H744 5V 25A
H745 -15V 10A
H754 +20V 8A and -5V 1A
H770 +15V 10A

DEC didn't waste any more money on regulators than necessary, so it is
a safe assumption that a fully configured system will use most of the
available DC power, which for just the +5V supplies alone is 1860W.

Fortunately the power supplies used with the H7420s are switchers, so they
are probably at least 65% efficient.

Eric
Received on Tue Sep 29 1998 - 03:25:42 BST